S1AP_Emulation: add missing create_cb

At the moment we do not have a default implementation for the create_cb.
The create_cb is called to resolve the vc_conn to which a subscriber
communication belongs in case it is not found in the S1apAssociationTable,
then it is resolved from an S1apExpectTable instead.

The current implementation uses the IMSI as key to resolve the vc_conn
from the S1apExpectTable, this might not work since in S1AP the UE
context is identfied by an MME_UE_S1AP_ID / ENB_UE_S1AP_ID pair.

Related: OS#5760
Change-Id: I758e7c8d8cc445cf18acdd7a25dcde8846fd84e5
diff --git a/mme/MME_Tests.ttcn b/mme/MME_Tests.ttcn
index 14965e6..a389c3d 100644
--- a/mme/MME_Tests.ttcn
+++ b/mme/MME_Tests.ttcn
@@ -141,18 +141,10 @@
 	return omit;
 }
 
-friend function S1apCreateCallback(S1AP_PDU msg, template (omit) MME_UE_S1AP_ID mme_id,
-				   template (omit) ENB_UE_S1AP_ID enb_id, charstring id)
-runs on S1AP_Emulation_CT return S1AP_ConnHdlr
-{
-	setverdict(fail, "implement this");
-	mtc.stop;
-}
-
 friend function f_init_one_enb(charstring id, integer num := 0) runs on MTC_CT {
 	id := id & "-S1AP" & int2str(num);
 	var S1APOps ops := {
-		create_cb := refers(S1apCreateCallback),
+		create_cb := refers(S1AP_Emulation.ExpectedCreateCallback),
 		unitdata_cb := refers(S1apForwardUnitdataCallback)
 	}
 	var S1AP_conn_parameters pars := {